Flame-resistant composition, and electrical product thereof

ABSTRACT

Flame-resistant composition comprising a cross-linked polyolefin, decabromodiphenyl ether, silicone gum and dibasic lead phthalate, and electrical conductors insulated therewith.

This application is a continuation-in-part of our previously filedapplication for patent Ser. No. 554,471, filed Mar. 3, 1975, of the sametitle and now abandoned.

BACKGROUND OF THE INVENTION

The increased use of polymeric compositions, such as polylefins, in manyand diverse applications or products, and the combustibility of suchpolymeric materials, has greatly stimulated the investigation offlame-proofing measures for polymeric compositions. Moreover, the highcosts of fire damage in lives and property, and the imposition ofincreasingly stringent safety regulations, have recently significantlyintensified the pursuit of more effective or practical means ofcontrolling or inhibiting combustion and the propagation thereof in manyproducts and materials.

Notwithstanding prior developments of a great number of flameproofingmeasures or additives resulting from this expanding effort, thereremains a continuing need for improvements to meet current or newrequirements in this area.

SUMMARY OF THE INVENTION

This invention comprises the discovery of the improved resistance toflame or combustion, and the propagation thereof, and other advantagesattributable to the combination of decabromodiphenyl ether, silicone gumand dibasic lead phthlate with cross-liked polyolefins, such aspolyethylene, and other ingredients. The invention thus relates toflame-resistant polyolefin compounds, and it has particular utility inflame-proofing electrical insulations comprising ethylenecontainingpolymer compounds which have been cross-link cured.

OBJECTS OF THE INVENTION

It is a primary object of this invention to provide polyolefin compoundsof improved resistance to flame and combustion, and deformation and flowat high or flame temperatures.

It is also an object of this invention to provide polyolefin compoundshaving improved electrical and physical properties, as well asresistance to flame and combustion.

It is a further object of this invention to provide an electricalconductor comprising a metallic conductive element having an insulationthereabout of a cross-linked polyolefin compound which is highlyresistant to flame and combustion and has superior electrical andphysical properties.

BRIEF DESCRIPTION OF THE DRAWING

The Figure comprises a perspective view of an insulated conductorcomprising a metallic element having a cross-linked polyolefininsulation thereabout.

DESCRIPTION OF A PREFERRED EMBODIMENT

In accordance with this invention, a cured polymeric compound having ahigh level of resistance to flame and combustion, and deformation andflow at high or flame temperatures, among other improved andadvantageous attributes, is provided with a polyolefin compositioncomprising cross-linked ethylene-containing polymers by combiningtherewith decabromodiphenyl ether, silicon gum and dibasic leadphthlate.

The polyolefin compositions of this invention compriseethylene-containing polymers such as polyethylene, copolymers ofethylene and other polymerizable materials, and blends of such polymersincluding copolymers. Typical copolymers of ethylene and otherpolymerizable materials include, for example, ethylene-propylenecopolymers and ethylene-propylene diene terpolymers, ethylene-vinylacetate, ethylene alkylacrylate copolymers, and ethylene-butenecopolymers.

The flame-resistant, cross-link cured polyolefin compound products ofthis invention can comprise fillers, pigments, curing coagents, andother conventional additives including preservatives such asantioxidants, modifying agents, mold release ingredients, processingaids or lubricants such as lead or zinc stearates in minuscule amountsof about 1 to 5 parts by weight, and the like which are commonlycompounded with polyolefins, in addition to the essential ingredients orbasic components thereof set forth hereinafter, such as thedecabromodiphenyl ether, silicone gum and dibasic lead phthlate.

The invention applies to and includes all of the above-referredpolyolefins when cross-link cured and thermoset by a heat-activatedperoxide cross-linking agent such as disclosed in U.S. Pat. Nos.2,888,424; 3,079,370; 3,086,966 and 3,214,422, or by irradiation.Suitable peroxide cross-link curing agents comprise organic tertiaryperoxides characterized by at least one unit of the structure: ##STR1##which decomposes at a temperature above about 295° F. and therebyprovide free radicals. Peroxide curing agents can be used in amounts ofabout 2 to 8 parts by weight per 100 parts of the polymer. A preferredperoxide is a di-α-cumyl peroxide, and other apt peroxides comprise thetertiary diperoxides such as 2,5-dimethyl-2,5-di (t-butyl peroxy) hexaneand 2,5-dimethyl-2,5-di(t-butyl peroxy) hexyne-3, and the like diperoxyand polyperoxide compounds. Also a curing coagent such as triallylcyanurate is preferably employed in amounts of up to about 5 parts byweight per 100 parts of the polymer. Radiation cross-link curing can beproduced by high energy electrons, X-ray and the like sources ofirradiation.

The organopolysiloxane gum or eleastomer of this invention, for use incombination with the polyolefin, decabromobiphenyl ether, and leadcompound, among other ingredients, comprises gums or organopolysiloxaneswhich have been condensed to a high molecular weight polymer of a gummyelastic, substantially semi-solid state. For example a typical siliconeelastomer for use in the composition of this invention is a class ofdimethylpolysiloxanes having the chemical structure: ##STR2##

Another class of silicone elastomers for use in this invention is themethyl-phenyl polysiloxanes. Further examples of the type of siliconeelastomer gums usable in obtaining the compositions of this inventioncomprise the organopolysiloxanes referred to in U.S. Pat. Nos. 2,888,424and 2,888,419, and identified in detail in U.S. Pat. Nos. 2,448,556;2,448,756; 2,457,688; 2,484,595; 2,490,357; 2,521,528; 2,541,137;3,098,836; and 3,341,489. Such high molecular weight siloxane polymersnormally have Brookfield viscosities of in excess of about 100,000centipoise at 25° C.

The lead component comprises dibasic lead phthlate, or equivalent leadcompounds.

The fumed silica comprises a form of silica described in U.S. Pat. No.2,888,424, and a type which is sold under the trade designation ofCabosil MS7 of Godfrey L. Cabot, Inc., of Boston, Massachusetts.

The combination of decabromodiphenyl ether, silicone gum and dibasiclead phthlate and other ingredients of this invention can be mixed andcombined with a polyolefin component by means of any conventionalcompounds method or apparatus, such as working in a Banbury mixer or ona two roll rubber mill. Preferably the ingredients of the compoundformulation, except those which are sensitive to the relative moderatemixing temperatures of about 300° F. to about 400° F., such as a heatdecomposable peroxide curing agent, are combined and initially admixedtogether or substantially uniformly dispersed with each other at atemperature sufficient to soften and plasticize the particularpolyolefin ingredient. Following the attainment of substantialuniformity of the admixed ingredients, the temperature of the admixedbatch is reduced below the decomposition level of the particularperoxide curing agent, or other heat sensitive ingredient, and thecuring agent or any other sensitive ingredient is then introduced anddispersed preferably uniformly in the mix.

The proportions of the flame-proofing combination of decabromodiphenylether, silicone gum, dibasic lead phthalate and the like ingredientsadmixed with the polyolefin compounds depend, of course, upon thedesired or required degree of resistance to flame and combustion, andthe content of polymeric or other combustible materials in the overallcompound. Suitable amounts for effective flame resistance in polyolefinscomprise about 15 to about 50 parts by weight of the decabromodiphenylether, about 3 to about 10 parts by weight of the silicone gum, andabout 3 to about 10 parts by weight of the dibasic lead phthlate, per100 parts by weight of the organic polymer content of the compound.However, greater or smaller quantities can suffice for particularapplications.

In accordance with this invention, the level of resistance to flame anddeformation or flow at high or flame temperatures provided by thecombination of decabromodiphenyl ether, silicone gum and lead, and otheringredients of this invention within a polyolefin compound can beenhanced by the inclusion of an oxide of antimony, such as antimonytrioxide, in the compound. Suitable amounts of such oxides of antimonyinclude about 5 to about 25 parts by weight per 100 parts by weight ofthe polyolefin polymer.

Typical formulations for the practice of this invention comprise, inapproximate relative parts by weight, the following combinations ofessential and preferred ingredients.

    ______________________________________                                        Ingredient            Parts by Weight                                         ______________________________________                                        Polyolefin            100                                                     Decabromodiphenyl ether                                                                             15-50                                                   Silicone gum           3-10                                                   Dibasic lead phthalate                                                                               3-10                                                   Antimony oxide         5-25                                                   Fumed silica           3-10                                                   Clay                   0-25                                                   Antioxidants           1-10                                                   Processing aid or molding lubricant                                                                 0-5                                                     Curing coagent        0-3                                                     Organic peroxide curing agent                                                                       2-5                                                     ______________________________________                                    

The following comprise examples of the novel and improved flameresistant polyolefin composition of this invention, with the ingredientsgiven in relative parts by weight.

The test specimens for each example were compounded in a typical manner,comprising combining all ingredients, except the peroxide curing agent,at a temperature of about 100° C. + 5° C. for about 5 minutes, thenadding and blending in the peroxide for another 5 minutes at the sametemperature, and curing the sample specimens thereof at 177° C. for 30minutes in a press. The composition of the specific formulation given inthe above mentioned example exhibited the properties set forth below:

    ______________________________________                                        INGREDIENTS              EXAMPLES                                                Parts By Weight       I       II                                           ______________________________________                                        Polyethylene             100     100                                          Decabromodiphenyl ether  40      25                                           Silicone gum             6.25    5                                            Dibasic lead phthalate   5       5                                            Antimony oxide           14      10                                           Fumed silica             5       5                                            Clay                     --      15                                           Antioxidants                                                                  Polymerized trimethyl dihydroquinoline,                                                                1.5     --                                           Agerite MA                                                                    4,4'-thiobis-(6-tert-butyl-m-                                                                          0.25    --                                           cresol), Santowhite Crystals                                                                           0.25    --                                           Thioester bis hindered-phenol, Irganox 1035                                                                    3                                            Thio dipropionate polyester, Poly TDP 2000                                                                     3                                            Processing aid                                                                Lead stearate            --      1                                            Vinyl silane             --      1.25                                         Curing coagent-triallyl cyanurate                                                                      1       1                                            Peroxide curing agent-dicumy peroxide                                                                  2.5     2.5                                          ______________________________________                                        PROPERTIES             EXAMPLES                                                                      I        II                                            ______________________________________                                        Oxygen Index Value     28.4     27.2                                          UL-44 FR-1 Flame Test  passed   passed                                        Original Tensile Strength, psi                                                                       2460     2233                                          Original Elongation, percent                                                                         400      376                                           Heat Treated 7 Day at 150° C                                           Percent Retention - Tensile, psi                                                                     88       99                                            Percent Retention - Elongation                                                                       91       90                                            Heat Treated 30 Days at 136° C                                         Percent Retention - Tensile, psi                                                                     89       92                                            Percent Retention - Elongation                                                                       88       80                                            Heat Treated 60 Days at 136° C                                         Percent Retention - Tensile, psi                                                                     89       99                                            Percent Retention - Elongation                                                                       82       82                                            Heat Treated 90 Days at 136° C                                         Percent Retention - Tensile, psi                                                                     55       60                                            Percent Retention - Elongation                                                                       34       19                                            ______________________________________                                    

The flame resisting properties of the examples of the compositions ofthis invention were all identically evaluated by the Oxygen Index Test(ASTM D-2863-7-) which designates the fraction of oxygen by volume innitrogen required to just maintain flaming of the material of the testsample. Thus, the higher the oxygen index for a composition, the betterits resistance to combustion and flame.

Referring to the drawing, there is shown a typical construction for aninsulated electrical wire or cable product 10*, comprising a metallicconductive element 12* and an overlying body of cured polymericinsulation 14* extending thereabout or covering the conductor. In thedrawing, the product 10* is illustrated as a short section with theinsulation 14* removed from the end portion of the conductor 12*.According to one embodiment of this invention, the novel flame-resistantpolyolefin thereof can be used to provide or form the insulation 14* onconductive element 12* of wire or cable product 10*. It is to beunderstood from the foregoing, however, that the insulation can comprisea coating on any portion of a conductive element and that the insulationneed not completely enclose the element where such is not necessary fora desired insulative effect.

Although the invention has been described with reference to certainspecific embodiments thereof, numerous modifications are possible and itis desired to cover all modifications falling within the spirit andscope of the invention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:
 1. An electrical conductor comprising a metallicconductive element having a flame-resistant, cross-link cured polyolefininsulation thereabout consisting essentially of the following, in theapproximate relative parts by weight of:

    ______________________________________                                        Polyolefin              100                                                   Decabromodiphenyl ether 15  - 50                                              Silicone gum            3 - 10                                                Organic lead salt       3 - 10                                                Antimony oxide          5 - 25                                                Fumed silica            3 - 10                                                ______________________________________                                    


2. The electrical conductor of claim 1, wherein the polyolefin iscross-link cured with a peroxide curing agent.
 3. The electricalconductor of claim 1, wherein the polyolefin comprises at least oneethylene-containing polymer selected from the group consisting ofpolyethylene, copolymers of ethylene and other polymerizable materials,and blends of such polymers.
 4. An electrical conductor comprising ametallic conductive element having a flame-resistant, cross-link curedpolyolefin insulation thereabout consisting essentially of thefollowing, in approximate relative parts by weight of:

    ______________________________________                                        Polyethylene               100                                                Decabromodiphenyl ether    40                                                 Silicone gum               6.25                                               Dibasic lead phthlate      5                                                  Antimony oxide             14                                                 Fumed silica               5                                                  Antioxidant                1.75                                               Triallyl cyanurate curing coagent                                                                        1                                                  Organic tertiary peroxide curing agent                                                                   2.5                                                ______________________________________                                    


5. The electrical conductor of claim 4, wherein the antioxidantcomprises about 1.5 parts by weight of polymerized trimethyldihydroquinoline and about 0.25 parts by weight of 4,4'-thiobis-(6tert-butyl-m-cresol).
 6. An electrical conductor comprising a metallicconductive element having a flame-resistant, cross-link cured polyolefininsulation thereabout consisting essentially of the following, inapproximate relative parts by weight of:

    ______________________________________                                        Polyethylene               100                                                Decabromodiphenyl ether    25                                                 Silicone gum               5                                                  Dibasic lead phthlate      5                                                  Antimony oxide             10                                                 Fumed silica               5                                                  Clay                       15                                                 Antioxidant                6                                                  Vinyl silane               1.25                                               Triallyl cyanurate curing coagent                                                                        1                                                  Organic tertiary peroxide curing agent                                                                   2.5                                                ______________________________________                                    


7. The electrical conductor of claim 6, wherein the antioxidantcomprises about 3 parts by weight of thioester bis hindered - phemol andabout 3 parts by weight of thio dipropionate polyester.